Bus duct assembly

ABSTRACT

In isolated phase bus duct, a circular bus bar is supported coaxially inside a circular housing by means of a number of annular insulators spaced along the length of the bus inside the housing. Each insulator is in the form of a collar having a mid ring portion with annular skirts on both ends. The insulator surrounds the bus and extends radially outward from it to the housing. An elastomeric ring surrounds the bus at either end of the insulator and is compressed lightly between the bus and the inner sloping surface of the inner skirt on the insulator by means of a number of tabs secured to the bus. The outer periphery of the insulator has an annular groove which contains an elastomeric ring compressed lightly between the insulator and the housing. These rings cushion the assembly and allow the bus to move towards its position of zero forces from short circuit currents. This reduces the short circuit stresses imposed on the assembly.

United States Patent [4 1 Apr. 4, 1972 Rehder BUS DUCT ASSEMBLY [72]Inventor: Robert H. Rehder, Peterborough, Ontario,

Canada [73] Assignee: Canadian General Electric Company Limited,Toronto, Ontario, Canada [22] Filed: Mar. 12, 1971 [21] Appl. No.:123,668

[52] U.S. Cl. ..174/16 B, 174/28, 174/99 B [51] Int. Cl. ..H0lb 9/04[58] FieldofSearch ..174/16R, 16B,99R, 99B,

[ 56] References Cited UNITED STATES PATENTS 3,573,341 4/1971 Graybill..174/28 X 3,546,356 12/1970 Graybill.... ..174/28 X 3,391,243 7/1968Whitehead ..174/28 FOREIGN PATENTS OR APPLICATIONS 1,944 l/1907 GreatBritain ..174/28 Primary Examiner-Laramie E. Askin Assistant ExaminerA.T. Grimley Attorney-J. Wesley l-laubner, William Freedman, Frank L.Neuhauser, Oscar B. Waddell and Joseph B. Forman [5 7] ABSTRACT Inisolated phase bus duct, a circular bus bar is supported coaxiallyinside a circular housing by means of a number of annular insulatorsspaced along the length of the bus inside the housing. Each insulator isin the form of a collar having a mid ring portion with annular skirts onboth ends. The insulator surrounds the bus and extends radially outwardfrom it to the housing. An elastomeric ring surrounds the bus at eitherend of the insulator and is compressed lightly between the bus and theinner sloping surface of the inner skirt on the insulator by means of anumber of tabs secured to the bus. The outer periphery of the insulatorhas an annular groove which contains an elastomeric ring compressedlightly between the insulator and the housing. These rings cushion theassembly and allow the bus to move towards its position of zero forcesfrom short circuit currents. This reduces the short circuit stressesimposed on the assembly.

4 Claims, 2 Drawing Figures PATENTEDAPR 4 I972 SHEET 1 [1F 2 anelongated, circular, rigid housing;

BUS DUCT ASSEMBLY This invention relates to isolated phase bus ductassemblies, and in particular to the insulating means employed forsupporting a conductor inside its housing. Its object is to provide arelatively simple bus duct assembly having good electrical andmechanical characteristics.

A bus duct assembly according to the invention consists of andelongated, circular, rigid conductor located inside the housing; and aplurality of insulators located inside the housing at spaced intervalsalong the conductor for supporting it in spaced coaxial relation withthe housing. Each insulator is in the form of a collar having a mid ringportion with annular skirts on both ends. The insulator surrounds theconductor and extends radially outward from it to the housing. Anelastomeric ring surrounds the conductor at either end of the insulatorand is compressed lightly between the conductor and the inner slopingsurface of the inner skirt on the insulator by means of a number of tabssecured to the conductor. The outer periphery of the insulator has anannular groove which contains an elastomeric ring compressed lightlybetween the insulator and the housing. These rings cushion the assemblyand allow the conductor to move toward its position of zero forces fromshort circuit currents. This reduces the short circuit stresses imposedon the assembly.

A better understanding of the invention may be had from the followingdescription taken with the accompanying drawings, in which:

FIG. 1 is a simple diagram of an isolated phase, three phase, bus ductassembly; and

FIG. 2 is a view showing an insulator of FIG. 1 and broken sections ofthe conductor and housing.

FIG. 1 illustrates a three-phase, bus duct system of the isolated phasetype. The system consists essentially of three like assemblies or runsA, B and C wherein a rigid conductor or bus bar is enclosed in a rigidmetal housing. There is a separate run for each phase, and it is usuallyquite long and frequently in more than one direction. The housings aresupported sideby-side on suitable structure and shown interconnected atselected points along their length by means of low resistanceconnections for purposes of mechanical reinforcement of the housings andof allowing currents induced in each housing to circulate around a loopdefined by the series combination of said housing and the other twohousings connected across its ends by the low resistance connections atthe ends. in each housing, the induced current flows longitudinallythereof in a direction opposite to the instantaneous current in itsassociated conductor 10. Allowing the induced currents to flow in thismanner reduces the amount of flux escaping from the housings, as isexplained in U.S. Pat. Re. 26,233-Skeats. Since phase A is typical ofthe three assemblies it only will be described in more detail withreference to FIGS. 1 and 2. As illustrated for phase A, each assemblyconsists of a rigid conductor supported inside a rigid housing 11 bymeans of a number of insulators 12 located inside the housing at spacedintervals along the conductor. in a preferred assembly, the conductor isa circular, thick-walled, aluminum tube and the housing a circular,thin-walled, aluminum tube larger in diameter than the conductor. Theinsulators support the conductor coaxially inside the housing so thatthere is a uniform radial space between the conductor and the housing,the radial spacing being selected in accordance with the conductorvoltage.

Referring now to FIG. 2, where the preferred embodiment of the inventionis shown, insulator 12 is in the form of a collar having a ring midportion 13 with one or more annular skirts on each end spaced apartradially, the ring and skirts being coaxial with the conductor. In thisFlG., two skirts l4 and 15 are shown on the left hand end of the ringand two skirts l6 and 17 on the right hand end of the ring in asymmetrical configuration. The inner skirts 15, 17 may or may not be ofthe same shape and dimensions as the outer skirts 14, 16. Insulator 12has an inner peripheral surface, or bore, 18 which is a loose fit aroundconductor 10 and an outer peripheral surface 19 which is a loose fitinside housing 11. Outer surface 19 is formed with annular groove 20midway of the axial length of the insulator. Groove 20 contains anannular elastomeric member 21 which is compressed somewhat between theinsulator and the housing. A pair of elastomeric members 22 and 23encircle the conductor under the inner sloping surfaces of skirts 15 and17, respectively, next to the inner peripheral surface 18. These membersare compressed somewhat between the insulator and the conductor. Thesize and the amount of compression of members 21, 22 and 23 is selectedso that, in effect, the insulator is held firmly in a centered positionby them, and they act as cushions between the insulator and theconductor and housing. This permits very limited relative movementbetween the conductor and the housing or of the insulator itself withoutimposing undue mechanical stresses on the insulator. The resilientmounting is particularly advantageous during short circuits because theconductor can now move toward its position of zero force, reducing theshort circuit stresses imposed on the assembly.

The position of zero force is an equilibrium position near the normalcentral position of the conductor into which the conductor tends to moveunder short circuit conditions and beyond which the conductor has nofurther tendency to move despite further increases in the magnitude ofthe short circuit current. This position is described and explained inmore detail in U.S. Pat. No. 2,892,012Swerdlow et al., where it isreferred to also as the zero force line position".

Insulator 12 may be a solid porcelain body glazed on its skirt surfacesor it may be a plastic body, as for example, a matte of glass fibersbonded together with an epoxy or a polyester resin. Members 22 and 23may be neoprene O-rings and member 21 a length of polyvinyl chloridehose, or tubing, coiled once around the insulator. The radial dimensionof the insulator determines the spacing of the conductor from thehousing and it is great enough to prevent strike-over between theconductor and the housing. The surface area of the skirts is greatenough to provide the creepage distance necessary.

Suitable means is provided for holding elastomeric members 22 and 23 inplace between the insulator and the conductor, whereby the insulator issecured to the conductor in a manner that blocks substantial axialmovement of the conductor relative to the insulator. In a preferred formof the invention, this holding means comprises two or more retainingtabs welded to the conductor at spaced intervals around it at either endof the insulator as illustrated at 24 and 25. The illustrated tabs arecurved plates, e.g., two semicircular plates for each member, abuttingthe elastomeric members 22 and 23 so as to compress them slightlybetween the conductor and the insulator and between the tabs and thetapered surfaces of the insulator. The retaining tabs are welded to theconductor along an edge 26 farthest from the insulator. There is usuallyno need to secure insulator 12 to housing 11 in runs having one or morebends in the run because the bends serve as means for transmittingforces axially of the conductor to the housing. It is, however, goodpractice to secure one insulator to the housing as well as the insulatorto the conductor in a straight run having a significant verticalcomponent of direction. This may readily be done by drilling three orfour small holes 27 through the wall of the housing at equally spacedintervals around the housing directly opposite elastomeric member 21,and driving a self-tapping screw 28 into each hole, the screw being longenough to penetrate tubing 21 and extend well into it. In a straightrun, only one insulator is secured to the housing; the others are notsecured to the housing, but are free to move with thermal expansion andcontraction of the conductor and housing.

The presence of elastomeric rings 22 and 23 makes it unnecessary toprovide a precise fit between the bore of insulator 12 and the outerperiphery of conductor 10 and thus facilitates assembly of eachinsulator about the conductor. In this respect, the bore of eachinsulator 12 is made sufficiently larger than the conductor to provide aclearance space between the bore and conductor periphery that permitsthe insulator to be easily slid into its proper position on theconductor without interference from minor surface irregularities anddespite minor size variations in these two parts. After the insulator isin its desired position, the elastomeric rings are positioned within thetapered portions of the insulator bore and are forced toward each otherto produce a wedging action that lightly compresses the rings betweenthe bore and the conductor, forcing them to take up the clearance spaceand to provide a connection between the insulator and the conductorwhich prevents significant axial movement of the conductor relative tothe insulator.

The presence of the elastomeric outer ring likewise facilitates assemblyof the housing 11 over the insulators 12. When the housing 11 is slippedover the insulator, the ring 20 yields slightly to accommodate surfaceirregularities and size variations between these two parts. Clearancespace between the insulator and the housing is taken up by theelastomeric ring.

While I have shown and described particular embodiments of my invention,it will be obvious to those skilled in the art that various changes andmodifications may be made without departing from my invention in itsbroader aspects; and I, therefore, intend herein to cover all suchchanges and modifications as fall within the true spirit and scope of myinvention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

l. A bus duct assembly comprising:

a. an elongated circular housing;

b. an elongated circular conductor located inside said housing coaxiallytherewith, said conductor having an outside diameter substantially lessthan the inside diameter of said housing;

c. at least one insulator located inside said housing and supportingsaid conductor, said insulator comprising a collar surrounding saidconductor and having a mid ring portion and at least one annular skirton each end of the ring portion surrounding said conductor, said collarhaving an inner and an outer periphery located near said conductor andsaid housing respectively;

d. a pair of first elastomeric rings surrounding said conductor atopposite ends of said inner periphery;

e. means for lightly compressing said elastomeric rings between saidconductor and said inner periphery;

. and an additional elastomeric ring surrounding the outer periphery ofsaid collar and positioned in lightly compressed relationship betweensaid outer periphery and said housing, said elastomeric rings allowinglimited radial movement between said conductor and said housing.

2. The bus duct assembly of claim 1 in which said collar has an annulargroove in said outer periphery in which said additional elastomeric ringis positioned.

3. The bus duct assembly of claim 2 in which said additional elastomericring is a one-turn length of tubing and in which a plurality of screwsare threaded through the wall of said housing into said tubing to securesaid insulator to said housing.

4. The bus duct assembly of claim 1 in which:

a. said inner periphery has tapered portions at its axially oppositeends against which said first elastomeric rings abut, and

b. said means for compressing said first elastomeric rings comprisesretaining structures secured to said conductor at the axially outersides of said first rings in positions that result in each of said firstrings being compressed between one of said retaining structures and oneof said tapered portions.

1. A bus duct assembly comprising: a. an elongated circular housing; b.an elongated circular conductor located inside said housing coaxiallytherewith, said conductor having an outside diameter substantially lessthan the inside diameter of said housing; c. at least one insulatoRlocated inside said housing and supporting said conductor, saidinsulator comprising a collar surrounding said conductor and having amid ring portion and at least one annular skirt on each end of the ringportion surrounding said conductor, said collar having an inner and anouter periphery located near said conductor and said housingrespectively; d. a pair of first elastomeric rings surrounding saidconductor at opposite ends of said inner periphery; e. means for lightlycompressing said elastomeric rings between said conductor and said innerperiphery; f. and an additional elastomeric ring surrounding the outerperiphery of said collar and positioned in lightly compressedrelationship between said outer periphery and said housing, saidelastomeric rings allowing limited radial movement between saidconductor and said housing.
 2. The bus duct assembly of claim 1 in whichsaid collar has an annular groove in said outer periphery in which saidadditional elastomeric ring is positioned.
 3. The bus duct assembly ofclaim 2 in which said additional elastomeric ring is a one-turn lengthof tubing and in which a plurality of screws are threaded through thewall of said housing into said tubing to secure said insulator to saidhousing.
 4. The bus duct assembly of claim 1 in which: a. said innerperiphery has tapered portions at its axially opposite ends againstwhich said first elastomeric rings abut, and b. said means forcompressing said first elastomeric rings comprises retaining structuressecured to said conductor at the axially outer sides of said first ringsin positions that result in each of said first rings being compressedbetween one of said retaining structures and one of said taperedportions.